Part of the present invention, the most economical approach for the removal of sulphur from fluid streams is through the use of amine addition. There are also a number of ways of removing hydrogen sulfide from hydrocarbon streams. The three most common methods employed include: (1) iron sponge processes; (2) hot potassium carbonates; and (3) amine addition. The iron sponge process requires low gas and hydrogen sulfide flowrates. It has a relatively low initial cost and also has high efficiency for gas streams with low hydrogen sulfide content. The hot potassium carbonate process can handle high gas rates and high hydrogen sulfide levels of 5% to 50%. The hot potassium carbonate process reduces hydrogen sulfide levels to less than 0.1%. The process is very stable and does not require extensive heat exchange equipment. The amine addition process utilizes monoethanolamine (MEA) and/or diethanolamine (DEA). The amine addition process can handle high gas rates and low to intermediate hydrogen sulfide levels (1% to 5%). The amine addition process can reduce hydrogen sulfide to less than 1 grain per 100 cubic feet. The iron sponge process is used primarily for natural gas desulfurization while the carbonate and amine processes are used in refinery processes.
Of these three processes, the amine addition process is the most popular since refinery waste gases generally have high hydrogen sulfide concentrations and a greater removal efficiency is obtained. Both DEA and MEA are used, with DEA being preferred since MEA is degraded by carbonyl sulfide and carbon disulfide in the gas streams.
Amine solutions will absorb both hydrogen sulfide and carbon dioxide according to the following reactions: EQU RNH.sub.2 +H.sub.2 S.revreaction.RNH.sub.3 HS EQU RNH.sub.2 CO.sub.2 +H.sub.2 O.revreaction.RNH.sub.3 HCO.sub.3
The absorption of hydrogen sulfide occurs at 100.degree. F. or below. The desorption of the sulfide from the amine happens at 240.degree. F. The amine desulfurization process involves contacting the sour gas stream with a cool amine solution to absorb the hydrogen sulfide and then regenerating the amine and stripping the hydrogen sulfide from the amine solution by heating. The hydrogen sulfide, removed from the gas stream, is either burned and converted to sulfur dioxide, converted to elemental sulfur using the Claus process, or the amine-sulfur salt is collected as marine bunker fuel and burned at sea.
Another process was developed by one of the inventors to the present application for the removal of sulfur from fluids or the sulfur from silver ore. This invention, described in U.S. patent application Ser. No. 08/151,911, filed on Nov. 15, 1993, and entitled "Composition and Process for the Removal of Sulfur from Silver" comprises a composition that includes a mixture of generally 33 weight percent sodium carbonate, 66 weight percent sodium chloride, and 0.02 weight percent of cayenne pepper in an aqueous solution. The aqueous solution includes two to six ounces of the mixture per gallon of water. The mixture can further include a non-oxidized aluminum material.
Another process, developed by Etzel and Shay, teaches a water purification process related specifically to reducing selenium and arsenic concentrations in contaminated water or wastewater streams. Iron loaded cation exchange resins, when contacted with contaminated water or wastewater streams, are effective for forming immobilized complexes with selenite and arsenate contaminants. The iron loaded resins can be easily regenerated by sequential treatment with acid and a solution of a soluble iron salt. In this process, selenium is primarily in the form of selenite. This process contacts the contaminated water or wastewater stream with a cation exchange resin, preferably a strong acid cation exchange resin. The selenite anions react with the resin complexed iron cations to form iron selenite complexes immobilized on the resin surface. To optimize the removal of selenium as selenite, the process includes the step of treating the contaminated water or wastewater stream to convert essentially all of the non-selenite selenium contaminants to selenite before contacting the water or wastewater stream with the iron (II)-complexed cation exchange resin. When a selenite-contaminated water or wastewater stream is passed through a bad of an iron (II)-complexed strong acid cation exchange resin, iron-selenite forms as an immobilized ionic complex on the surface of the cation exchange resin resulting in a treated water or wastewater stream having a reduced selenium concentration. The iron complexed cation exchange resin is readily regenerated for re-use by contacting it with an acid (to release the iron selenite complex and form the acid state of the resin) and thereafter with a solution of a water soluble iron salt.
Another prior process has employed fine mesh magnetized ion exchange resins for water softening (exchanging calcium and magnesium ions for sodium ions). This process, developed by Etzel and Wachinski, one of the present co-inventors, uses less than 20 micron diameter fine mesh magnetized ion exchange particles in a columnar operation. The particles are formed by encapsulating a core of magnetic material in an ion exchange resin. The particles are magnetized and disposed in a column where they attach to magnetic mesh retention means, such as stainless steel wool. The design of the column permits use of the fine mesh ion exchange particles and their properties of rapid exchange rates and efficient utilization of resin capacity, while avoiding the prior problems of plugging, fouling, and excessive pressure drop.
Various U.S. patents have issued in the past concerning processes for the removal of contaminants from a fluid stream. U.S. Pat. No. 2,798,580, issued to Voigtman, discloses a coated felted or bat-type fibrous material such as cellulosics, glass, or asbestos with various ion exchange resins to increase their exchange capacity. Others have encapsulated magnetic particles in ion exchange resins. Examples of this are Weiss et al., U.S. Pat. No. 3,560,378, Turbeville, U.S. Pat. No. 3,657,119, and Weiss et al., U.S. Pat. No. 3,890,224. Weiss at al. '378 recognized the problems that fine ion exchange resins exhibited such as excessive pressure drop, quick fouling, and loss through entrainment. The solution in this patent was to use the encapsulated resins in an agitated mixer system during liquid treatment and then to magnetically coalesce the resin particles after treatment. The Weiss patent did not purport to solve the problems associated with fine mesh resins when used in a fixed-bed process. They did compare the reaction kinetics of gamma iron oxide particles encapsulated with trimethylol phenol N,N his (3-amino propylmethylamine) having a particle size range of 250-500 microns with a standard size 350-1200 micron resin in fixed bed operation and found them to be substantially the same.
Svyadoshich et al. in "Wastewater Purification Using Superparamagnetic Dispersed Ion Exchanger In Constant Magnetic Field", 10 Soviet Inventions Illustrated 2, Nov. of 1976, taught a column surrounded by an electromagnetic coil which produces a magnetic field of 350 Oersted and a super-paramagnetic cation exchange resin 40-60 microns in diameter to obtain ion exchange rates eight times faster than conventional size resins.
In the field of water purification, attempts have been made to use high-gradient magnetic fields to separate and extract weakly paramagnetic submicron particles from fluid streams. DeLatour and Kolm, "High-Gradient Magnetic Separation: A Water Treatment Alternative", in the Journal of American Water Works Association of Jun. 1976 discloses a number of suggestions for separation, including possible use of a matrix of stainless steel wool in a column under the influence of a magnetic field to capture and hold magnetic particles from a fluid stream.
Until the invention by Wachinski and Etzel, none of the above-mentioned prior art disclosures satisfactorily solved the problems associated with fine mesh resins in fixed-bed columnar operation. Wachinski and Etzel's process increased the efficiency of the ion exchange processes in fixed-bed columnar operation while avoiding the problems associated with fine mesh ion exchange resins when used in such columns. The Wachinski and Etzel's process was specific for the use of fine mesh resin as a traditional ion exchanger to reduce the concentration of calcium and magnesium ions. This process had no application to processes involved in the reduction of contaminants in all fluid streams (compressible and non-compressible) utilizing immobilized metal complexes.
It is an object of the present invention to provide an apparatus and method for the effective removal of contaminants from a fluid stream.
It is another object of the present invention to provide an apparatus and method that allows for the regeneration of the contaminant-removing materials.
It is a further object of the present invention to provide a method and apparatus that is cost effective, efficient, and effective.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.